Electric-motor brake actuator of a motor vehicle parking brake

ABSTRACT

A particularly cost-effective electric-motor brake actuator which is useable in a highly flexible manner in respect of structural boundary conditions has an integrally formed cup which is equipped with a permanent magnet assembly and can be equipped with a separately manufactured, electromagnetic rotor assembly. In this manner, the equipment outlay is reduced as is the construction costs.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to the electric-motor brake actuator of a motorvehicle parking brake.

In order to be able to use a structurally small, high speed productionmotor that has a correspondingly small torque, the actuator is equippedwith a high-ratio reduction gear for actuating the brake. DE 1 97 48 318C1 discloses for this purpose a two stage gear train in which the firstreduction stage is provided as a toothed belt transmission between themotor and a second reduction stage in the form of an extremelyhigh-ratio, self-locking shaft gear or squash plate mechanism forcorrespondingly greatly increasing the output torque at the actuatoroutput. It is of advantage that the belt drive is as a reduction stagein the actuator because the motor axis and the transmission axis can bearranged parallel to one another, which produces an overall compactconstruction. Fundamentally, however, a construction of this type canalso be achieved by means of a multi-stage conventional gear mechanism.A spindle is connected to the output shaft of a gear motor actuator ofthis type for the purpose of adjusting the mechanical brake system in aself-locking manner (namely for applying or releasing said mechanicalbrake system).

It is known from DE 1 00 64 803 C1 to install the fully functionalmotor, which is encapsulated in a housing, in a receiving device, whichtapers in a slightly conical manner, in the actuator and to lock saidmotor in a non-positive manner or preferably a positive manner toprevent said motor from turning.

The construction of a motor of this type is described for instance inU.S. Pat. No. 6,982,511 B2. A shaft stub of the rotor shaft is initiallyequipped in an axial manner with a bearing supporting ring and then witha ball bearing. The rotor that is equipped in this manner is lowered,with the ball bearing first, in an axial manner into a hollowcylindrical motor housing and in so doing the ball bearing is installedin a receiving device in the housing base. A pole sleeve that isequipped inside with stator magnets is pressed between the rotor and thehousing wall in an axial manner into the housing. A longitudinal slit inthe sleeve to provide said sleeve with radial elasticity is explicitlyrejected because the assembly process of said sleeve would then be toocomplicated and the magnetic flux guide would be interrupted. The ballbearing is fixed in an axial manner at the housing base by virtue of thefact that the end face of the sleeve rests against the bearingsupporting ring. Barbed hooks that are pushed out of the outer wall ofthe sleeve in a radial manner clamp the sleeve in the motor housing andas a measure to prevent said sleeve from being withdrawn from saidhousing engage into the inner wall of the motor housing, which incontrast is made from a soft material. The self-contained motor iscomplete and can now be installed in a conventional manner for instanceinto an actuating drive, in particular for auxiliary equipment in motorvehicles. This applies accordingly for the small motor previously knownfrom DE 10 2006 050 166 A1 that comprises a stator sleeve for receivingthe rotor, wherein the stator sleeve is made from a magnetically softsintered material and its inner wall is equipped with a pair of mutuallydiametrically opposite-lying permanent magnets having a differentpolarity and being made from a magnetically hard sintered material. Therotor bearing is also received in the base of a motor housing that isclosed in a cup-shaped manner at one end and is also used in this caseas the stator; as a result of which the motor is completelyself-contained ready for installation. According to DE 1 03 54 969 A1, apreviously completed small motor is installed in the transmissionhousing of a piece of equipment. Once the electromagnetic rotor has beenaccommodated in the sleeve-shaped motor housing of said small motor, thetwo end faces of said sleeve-shaped motor housing are equipped withbearing shields for the rotor shaft. A radially expandable flux ringthat is equipped on its inner wall with magnets rests against thehousing inner wall. This group of permanent magnets, flux ring and motorhousing is encased by means of injection-molded synthetic material forthe purpose of mechanically fixing said parts with respect to oneanother. Whereas the rotor shaft is equipped on the output side upstreamof the bearing shield with a toothed wheel, the rearward shaft stubsupports upstream of its bearing shield a brush commutator that is notfurther disclosed with respect to details. In the case of a similarmotor installation in accordance with U.S. Pat. No. 6,522,042 B1, statorpermanent magnets are integrally cast on a ring using aninjection-molding process and in so doing are anchored in apositive-locking manner in profiles that are formed from the ring.According to U.S. Pat. No. 5,268,607, the cup-shaped motor housing isspray-coated with glass-fiber-reinforced and mineral-filled syntheticmaterial in the case of a bearing seat that is formed downstream of thecup base; with a flux ring that is injection-molded onto the cup innerwall and two half shell-shaped permanent magnets are mounted in saidflux ring. This self-contained motor can be lowered into the supportplate of transmission housing for a vehicle windscreen wiper and cansubsequently be screwed to diametrically protruding holed ear-shapedflanges. The hermetically-housed direct current motor according to U.S.Pat. No. 3,772,546 having a permanent magnetic stator is likewiseequipped on the output side with a brush commutator.

In contrast thereto, U.S. Pat. No. 6,0617,746 B1 describes for a motorstator radially and axially mutually offset electromagnets having coilcores and pole shoes that are formed from magnetically soft powder.

BRIEF SUMMARY OF THE INVENTION

The two motor types referred to above can be installed as self-containedsmall motors in each case in the receiving chamber in the previouslymentioned injection-molded housing and can be connected by means of abelt drive or toothed wheel to the reduction gear that is likewisemounted in this actuator housing. In contrast thereto, the object of thepresent invention is to solve the technical problem of reducing theequipment outlay and as a consequence also the costs for theconstruction of an electric-motor brake actuator that is to be equippedwith a motor.

This object is achieved in accordance with the essential featuresdisclosed in the main claim. Accordingly, a fully functional motor is nolonger installed in a neutral housing receiving device for the purposeof constructing the actuator; but rather in this case only a separatelyproduced and delivered rotor is installed in a cup that is embodied in ahousing part and has been equipped in advance with a magnet assembly. Amagnet assembly of this type comprises (at least) two hollow cylindricalshells made from a permanent magnetic material that has a peripheralalternating polarity, wherein it is preferred that the shells are madefrom injection-molded sintered magnets. Said hollow cylindrical shellscan be held radially outside a sleeve-shaped sheet metal ferromagneticflux guide but are preferably arranged radially inside the sheet metalflux guide. This hollow cylindrical sheet metal flux guide is providedin an expedient manner with slits over at least a part of itsaxis-parallel length along a generating in order to be able to installsaid sheet metal flux guide in the cup more easily, namely with lessresilient elastic radial compression, in that the sheet metal flux guiderelaxes in such a manner that its diameter increases and as aconsequence it is held radially on the inner peripheral surface of thecup in a non-positive manner or by means of a material connection,namely fixedly clamped or preferably fixedly adhered thereto.

The adjacent end face of the motor shaft is mounted on the cup base. Themounting can be performed in a simply designed bearing shield that isinserted in or placed on the region of the cup opening which can bemounted axially opposite. As an alternative or in addition thereto, therotor shaft can also be mounted opposite the cup base outside the cup,namely in a separate, vibration-damped bearing bridge that is held bythe housing, or also directly in the housing cover or transmission coverlying opposite.

In any event, it is then expedient for a direct current motor operationif the mentioned bearing shield is omitted in order to arrange theelectromechanical or sensor-controlled electronic commutators towardsthe cup base.

Additional modifications and further alternatives within the scope ofthe present invention are evident in the further claims and, also withrespect to their advantages, in the description herein under of apreferred embodiment for achieving the object in accordance with theinvention, said exemplified embodiment being illustrated greatlyenlarged and not true to scale whilst being limited to the essentialfunctions of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The single FIGURE of the drawing illustrates in a sectional view aconstruction in accordance with the invention of an actuator of thegeneric type in the axial longitudinal sectional view but withouttechnical details relating to the transmission and without taking intoconsideration the electrical connections.

DESCRIPTION OF THE INVENTION

It is possible in the sectional illustration of the housing part 11 thatis part of a brake actuator 36 and can be produced from injection-moldedsynthetic material to roughly distinguish successive parts from oneanother: a drive region 12, a transmission region 13 and an outputregion 14 that is connected to the mentioned actuating spindle for thepurpose of actuating the brake. The motor shaft and wheel shaft aremounted in a gear box 15. A bearing bridge can be installed for thispurpose in said gear box in a vibration-damping and consequentlynoise-damping manner; for the purpose of simplifying the illustration,one bearing is illustrated in the housing cover 16 as is evident indetail by way of example in WO 2006/094804 A1.

In place of the self-contained fully functional small motor that isconventionally installed in the actuator housing part 11, a cup 17 thatis open towards the housing cover 16 is provided in this case in thehousing part 11. A permanent magnetic magnet assembly 18 is installed inthis cup 17 in a sleeve-shaped coaxial manner. Said assembly provides onthe periphery, in the circumferential direction, a sequence of (at leasttwo) alternating magnetic poles 19 (in this case 19+ and 19−). The poles19 are preferably illustrated by corresponding multiple permanentmagnetic elements 20 (in this case two such elements are arrangeddiametrically opposite one another with respect to the middle axis ofthe cup 17, spaced apart from one another on the periphery and as aconsequence following one another with spaces in between). Elements 20of this type are preferably injection-molded sintered magnets in theform of shells that have for instance a hollow cylindrical shape. Saidshells are expediently provided at the rear with a sheet metalferromagnetic flux guide 21 that as illustrated is in the form of acircumferential band. Said sheet metal flux guide can be supported underradially resilient elastic stress lying against the inner peripheralsurface 22 of the cup 17. The per se annular closed sheet metal fluxguide 21 can comprise for this purpose a particularly axis-parallellongitudinal slit 23 so that said sheet metal flux guide can be by wayof example manually radially compressed for the purpose of beinginserted into the cup 17; the said elements 20 are fixed on the innerperiphery of the per se annular closed sheet metal flux guide 21 in apositive locking manner or by means of a material connection. Thiscauses elastic flexural loadings of the sheet metal flux guide 21 tooccur between mutually adjacent elements 20, said loadings beingsufficient to expand said sheet metal flux guide radially outwards as itrelaxes after being inserted into the cup 17 and as a consequence torelax in any case slightly against the inner peripheral surface 22 ofsaid cup. In an expedient manner, the sheet metal flux guide 21 becomesadhered to the inner peripheral surface 22 of the cup 17; for whichpurpose it is useful to exert temporary additional pressure on theelements 20 in the centrifugal direction.

A central blind hole 24 at the, preferably in the, cup base 25 isequipped with a bearing 26 for the purpose of receiving the lower freeend face 27 of a coaxial shaft 28. Said coaxial shaft is a component ofan externally pre-assembled electromagnetic rotor assembly 29 havingarmature arms 30 and their magnetic coils 31. The upper region, orrather possibly the end face 33, of the shaft 28 is received by abearing 32 on the actuator cover 16 in the case of a separate, incontrast offset, bearing bridge (not illustrated) and/or on a bearingshield 37, (said upper region being the region that lies axiallyopposite the lower region).

Conventionally, sensors or rather the collector brush arrangements forelectronic or electromechanical commutation where the motor is operatingwith direct current are arranged on the output side (i.e. lying at thetop in the drawing), namely in part rotor-fixed and in the other partstator-fixed for instance on a bearing shield 37 in the opening plane ofthe cup 17. In particular, if a bearing shield 37 is not installedwithin the scope of the present invention, a commutation device of thistype is expediently arranged as a pre-assembled commutator assembly 34in the inside towards the base 25 of the cup 17, as schematicallyconsidered in the drawing. The stationary part of the commutatorassembly 34 can latch in a non-rotatable manner as it is being insertedinto the cup 17.

A particularly cost-effective gear-driven brake actuator 36 that canalso be used in a highly flexible manner in respect of structuralboundary conditions therefore comprises an electric-motor drive, whosestator magnet assembly 18 together with, if necessary, the commutatorassembly 34 is lowered, in particular latched or adhered, directly intoan actuator cup 15 to form an integral component of an actuator housing11. The cup 15 can be equipped with an externally assembled rotorassembly 29. Bearings 32 for the drive shaft and transmission shaft 28can be provided, apart from in the housing part 11 itself, in a bearingbridge that is mounted in or on the housing part 11 in avibration-damped and consequently noise-damped manner.

LIST OF REFERENCE NUMERALS

-   11 Housing part (of 36)-   12 Drive region (of 11)-   13 Transmission region (of 11)-   14 Output region (of 11)-   15 Gear box (of 11)-   16 Cover (of 11/15)-   17 Cup (on 15)-   18 Magnet assembly (in 17)-   19 Magnet poles (10+, 19−; of 20)-   20 Permanent magnetic elements (of 18)-   21 Sheet metal flux guide (of 18 between 20 and 22)-   22 Inner peripheral surface (of 17)-   23 Longitudinal slit (in 21)-   24 Blind hole (in 25)-   25 Base (of 17)-   26 Bearing (on or in 24)-   27 Lower end face (of 28 in 26)-   28 Shaft (of 29)-   29 Rotor assembly (inside 20)-   30 Armature arm (of 29 on 28; not illustrated in the drawing)-   31 Magnetic coils (on 30, not illustrated in the drawing)-   32 Bearing (in or on 16, for 33)-   33 Upper end face (of 28, in 32)-   34 Commutator assembly (below 37 or below 29)-   35 Motor (comprising 18+29+34+possibly 37)-   36 Actuator (with 11 and 35)-   37 Bearing shield (for 28 in 17)

The invention claimed is:
 1. An electric-motor actuator, comprising: acover; a housing part produced from an injection-molded syntheticmaterial and having a drive region, a transmission region, an outputregion, and a cup provided in said drive region, said cup openingtowards said cover and having an inner peripheral surface and a cupbase; a gear box disposed in said housing part; wheel shafts mounted ina case of a two-sided bearing configuration on one side in said gear boxand on the other side in said cover; a permanent magnet assembly held onsaid inner peripheral surface in a sleeve-shaped manner, said permanentmagnet assembly having at least two permanent magnetic elements ofalternating polarity of magnetic poles, said permanent magnetic elementsbeing disposed adjacent to one another spaced apart on a periphery, saidpermanent magnet assembly further having a sheet metal ferromagneticflux guide, said permanent magnetic elements are provided at a rear withsaid sheet metal ferromagnetic flux guide; and an electromagnetic rotorassembly disposed in said permanent magnet assembly and mounted on saidcup base, said electromagnetic rotor assembly having a shaft with anupper end face lying opposite a lower end face, said electromagneticrotor assembly inserted in a coaxial manner by said upper face end ofsaid shaft being received outside said cup in said cover.
 2. Theactuator according to claim 1, wherein said electromagnetic rotorassembly has in a vicinity of said cup base a commutator assembly. 3.The actuator according to claim 1, wherein said cup has a cup openingformed therein and axially opposite said cup base; and furthercomprising a bearing shield, said electromagnetic rotor assembly ismounted in said bearing shield in a region of said cup opening.
 4. Theactuator according to claim 1, wherein said permanent magnetic elementsare injection-molded sintered shells.
 5. The actuator according to claim1, wherein said permanent magnetic elements are fastened to said sheetmetal ferromagnetic flux guide in a form-locking manner or by means of amaterial connection.
 6. The actuator according to claim 1, wherein saidsheet metal ferromagnetic flux guide is supported against said innerperipheral surface of said cup in a radially resilient elastic mannerand is connected thereto by means of a material.
 7. The actuatoraccording to claim 1, wherein said sheet metal ferromagnetic flux guidehas an axis-parallel longitudinal slit formed therein.
 8. The actuatoraccording to claim 1, further comprising: a bearing shield; and acommutator assembly disposed on said bearing shield in a region of anopening plane of said cup.